ALBUMIN ATES AND OTHER PROTEIDS. 503 



Class III. Derived Albumins (Albuminates). 



(1-) Acid- Albumin or Syntonin. When proteids are dissolved in the stronger 

 acids, e.g., hydrochloric, they become changed into acid-albumins. They are 

 precipitated from solution by the addition of many salts (NaCl, Na 2 S04) or by 

 neutralisation with an alkali, e.g., sodic carbonate, but they are not precipitated 

 by heat. The concentrated solution gelatinises in the cold, and is redissolved by 

 heat. Syntonin, which is obtained by the prolonged action of dilute hydrochloric 

 acid (2 per 1000) upon minced muscle, is also an acid-albumin. It is formed also 

 in the stomach during digestion. According to Soyka, the alkali- and acid- 

 albumins differ from each other only in so far as the proteid in the one case is 

 united with the base (metal) arid in the other with the acid. 



(2.) Alkali- Albumin. If egg- or serum-albumin be acted upon by dilute 

 alkalies, a solution of alkali-albumin is obtained. Strong caustic potash acts upon 

 white of egg and yields a thick jelly (Lieberkiihn). The solution is not precipitated 

 by heat, but is precipitated by the addition of an acid. 



(3. ) Casein is the chief proteid in milk (p. 466). It is precipitated by acids and by 

 rennet at 40C. In its characters it is closely related to alkali-albuminate, but, 

 according to 0. Nasse, it contains more N. It contains a large amount of phos- 

 phorus (O'SS per cent.). It may be precipitated from milk by diluting it with 

 several tunes its volume of water and adding dilute acetic acid, or by adding 

 magnesium sulphate crystals to milk and shaking vigorously. Owing to the large 

 amount of phosphorus which it contains, it is sometimes referred to the nucleo- 

 albumins. When it is digested with dilute HC1 (O'l per cent.) and pepsin at the 

 temperature of the body, it gradually yields nuclein. 



Class IV. Fibrin. 



For fibrin, see p. 39, and for the fibrin-factors, p. 43. 



Class V. Peptones. 



For peptones and propeptones, see p. 331. 



Class VI. Lardacein and Other Bodies. 



There fall to be mentioned the "yelk -plates," which occur in the yelk: 

 Ichthin (cartilaginous fishes, frog) ; Ichthidin (osseous fishes) ; Ichthulin (salmon) ; 

 Emydin (tortoise Valenciennes and Fremy); also the indigestible Amyloid substance 

 (Virchow) or lardacein, which occurs chiefly as a pathological infiltration into various 

 organs, as the liver, spleen, kidneys, and blood-vessels. It gives a blue with iodine 

 and sulphuric acid (like cellulose), and a mahogany-brown with iodine. It is 

 difficult to change it into an albuminate by the action of acids and alkalies. 



Class VII. Coagulated Proteids. 



When any native albumins or globulins are coagulated, e.g., at 70C. , they yield 

 bodies with altered characters, insoluble in water and saline solutions, but soluble 

 in boiling strong acids and alkalies, when they are apt to split up. They are 

 dissolved during gastric and pancreatic digestion to produce peptones. 



Appendix: Vegetable Proteid Bodies. 



Plants, like animals, contain proteid bodies, although in less amount. They 

 occur either in solution in the juices of living plants or in the solid form. In com- 

 position and reaction they resemble animal proteids. Vegetable proteids have fre- 

 quently been obtained in a crystalline form (Radlkofer), e.g., from the seeds of 

 the gourd (Griibler) and various oleaginous seeds (Ritthausen). 



